A significant proportion of the mobile users worldwide are prepaid users, having a pre-paid subscription with an operator. These users are required to do a refill (or top-up or replenishment) of their account in order to be able to use the prepaid subscription. It is also possible that a time limit is defined for the service, such that a refill must be done within a certain time period or else the prepaid account can no longer be used for calls. An operator could check the subscriber's account before allowing the subscriber to engage in a session and also to stop a session when the balance is depleted.
A number of possibilities exist for performing a refill for a prepaid user, for example using a voucher or a credit card or via a banking service on the Internet.
Some of these possibilities to do a refill are combined with the prepaid user performing some aspect of a voice call. One option available in current mobile networks is that the prepaid user is given the option to do a refill when a request to setup a call is done. Another available option is to give the user the option to do a refill when an established call has been cleared due to an empty account. In current mobile networks these services are often realized by using CAMEL (Customized Applications for Mobile Enhanced Logic) to a charging system which handles the service.
The CAMEL standard forms part of the GSM Network (ETSI) and the 3rd Generation Partnership Project (3GPP) specifications. CAMEL service triggers are defined and accessible by the Mobile Switching Center (MSC) in a GSM network. For example, when the MSC receives a call diversion request from a user and a corresponding CAMEL trigger is defined for the diverting user, the MSC contacts a CAMEL service using a CAMEL Application Part (CAP) request. The CAMEL service then provides the appropriate service for the call, such as call forwarding or diversion, for example.
The present applicant has appreciated that there is no solution for these services for mobile prepaid users in an IMS network when the interface between the MMTel AS and the OCS is Ro. In this respect. Ro is a Diameter interface which will now be briefly explained with reference to FIG. 6 of the accompanying drawings, in the context of other such interfaces.
FIG. 6 illustrates the IMS entities and interfaces involved with online and offline charging systems.
Ro is a Diameter interface used by the AS, MRFC, S-CSCF (or more generally nodes in a service network) to exchange online charging information with the OCS.
Gx is a Diameter interface used to exchange policy decisions-related information between the PCEF and PCRF.
Gy is a Diameter interface between the OCS and PCEF (or more generally nodes in a core network).
The user is charged for voice and video via the Ro interface and for data via the Gy interface. (Gy is used for flow based charging).
Rx is a Diameter interface used to exchange policy and charging related information between the P-CSCF and PCRF.
Rf is a Diameter interface used to exchange offline charging information with the CDF
A functionality is covered in RFC 4006 (Diameter Credit Control) by including in a Final-Unit-Indication AVP the possibility to define Redirect as Final-Unit-Action and include a Redirect-Server AVP. The procedure described in RFC 4006 is called “graceful service termination” and covers only the case of replenishment after the final units have been consumed or for a new request and the account is empty (FUI included but no quota). The charging session remains during the replenishment and a new CCR(U) is sent to OCS after the replenishment.
However, with a solution only based on the use of FUI AVP, it will not be possible to create replenishment services for prepaid users which will give the user the same service level or better compared with the service in current mobile networks. The solution in RFC 4006 is more applicable to data than to MMTel services e.g. voice.
As well as RFC 4006 mentioned above, reference should also be made to RFC 3588 (Diameter Base Protocol), 3GPP TS 24.229 (Internet Protocol (IP) multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3), 3GPP TS 32.260 (IMS Charging), 3GPP TS 32.240 (Charging architecture and principles), 3GPP TS 32.299 (Telecommunication management; Charging management; Diameter charging applications).